Your processor is idling less in between executing code. Your CPU pushes out instructions to your GPU to actually render onto your screen. Therefore you WILL end up with higher CPU utilization, and higher GPU utilization. And guess what that means? It means more heat putting out. Because your GPU and CPU are now working harder. You are expending more energy, because you are doing more in the same period of time.
/*Slightly off topic: You should read up how hyper-threading works, because it essentially takes advantage of the downtime between execution of code.*/
I'm not as harsh as diceman2037, and don't agree with personal attacks like he did, but these are fundamentals of how a computer operates, and even physics.
13Mhz on the GPU wouldn't ever be the performance difference of 200% of the previous performance in something like Star Swarm.